Defect inspection device and defect inspection method

To detect an infinitesimal defect, highly precisely measure the dimensions of the detect, a detect inspection device is configured to comprise: a irradiation unit which irradiate light in a linear region on a surface of a sample; a detection unit which detect light from the linear region; and a signal processing unit which processes a signal obtained by detecting light and detecting a defect. The detection unit includes: an optical assembly which diffuses the light from the sample in one direction and forms an image in a direction orthogonal to the one direction; and a detection assembly having an array sensor in which detection pixels are positioned two-dimensionally, which detects the light diffused in the one direction and imaged in the direction orthogonal to the one direction, adds output signals of each of the detection pixels aligned in the direction in which the light is diffused, and outputs same.